ABSTRACT: PROJECT 3 Exposure to inorganic arsenic (iAs) affects large human populations worldwide and leads to a number of human diseases, including diabetes. Project 3 addresses a fundamental gap in understanding mechanisms underlying iAs-induced diabetes ? specifically the role of the gut microbiome. The association between iAs and diabetes has been established in numerous epidemiological studies. We and others have also demonstrated that iAs induces dysregulation of glucose and insulin metabolism in mice. The gut microbiome has a profound effect on human health through its key role in metabolic regulation, and emerges as a promising target for intervention and therapeutic treatment in human health. Accumulating evidence supports the role of the gut microbiome and Farnesoid X receptor (FXR) in the pathogenies and prevention of diabetes in both animals and humans. Our studies are among the first to demonstrate the functional interactions between iAs and the gut microbiome. Still, precisely how the iAs-altered gut microbiome affects diabetes risk remains to be determined. In particular, the molecular mechanisms underlying iAs-microbiome-host crosstalk are largely unknown. This represents a significant gap in iAs-microbiome research, which also impedes mechanism-based interventions to reduce arsenic-induced diabetes via targeting the gut microbiome and its metabolic functions. Our central hypothesis is that modulation of the gut microbiome will serve as a method for reduction of iAs-perturbed metabolic dysfunction/diabetes. Specifically, iAs-altered gut microbiome disrupts bile acids to inhibit FXR, which in turn alters gluconeogenesis and insulin signaling. Our robust preliminary data underscore the key role of microbiome- bile acid-FXR axis in iAs-induced diabetes, and highlight the potential to modulate iAs toxicity by targeting FXR via microbiome. To test this hypothesis, we will pursue three specific aims: Aim 1: Establish the functional link between altered gut microbiota and iAs-impaired bile acid metabolism; Aim 2: Determine the effects of inhibited FXR activation, driven by iAs-induced gut microbiome dysbiosis, on gluconeogenesis and insulin signaling; and Aim 3: Mediate iAs-induced diabetes via restoring FXR activation by gut microbiome manipulation. Our strong team (Drs. Lu, Sartor, Styblo and McDermott) has complimentary expertise in iAs toxicity, gut microbiome, iAs metabolism and iAs-induced diabetes. We use innovative techniques to characterize largely unknown contributions of gut microbiome-bile acid-FXR in iAs-induced diabetes and the project is in line with the theme of the UNC-SRP ?Identifying novel methods to reduce iAs exposure and elucidating mechanisms underlying iAs- induced metabolic dysfunction with a vision for disease prevention.? The highly modifiable nature of the gut microbiome and in-depth mechanistic understanding of the role of microbiome in disease will allow us to develop new tangible approaches to reduce iAs-induced diabetes by targeting the gut microbiome and related signaling molecules.